The 20 year judgement lien was created by federal law in 1994.  Prior to that time the statute covered 10 years.  I've talked to so many abstractors that are completely confused and often mistake the judgement lien for the tax lien...but they are completely different instruments. 

In order to insure we cover our bases, we check the index back 20 years for each owner of record as of 1994 (owners of record from 1984 to the date the law passed were exempt as of the date the law passed).  As time passes, that list will increase obviously.  Of course, many of our counties are quite small so it's easier to check the the USA as plaintiff. 

One caveat...you have to know where these judgements are filed.  In another county we search, the judgement is filed in the tax lien book at the ROD and not in the clerk's office.  Unfortunately, most abstractors only search the lien book for 10 years.